A heat-sensitive recording process has recently been widely used in the fields of facsimile recording and printers, since the process has such advantages as (1) a liquid development treatment is unnecessary, (2) when the support for the heat-sensitive recording material is paper, the quality of the paper support may be that of an ordinary paper, (3) the process can be easily handled, (4) the coloring density is high, (5) the recording device for the recording process is simple and inexpensive, (6) the process does not generate noise during recording, etc. As heat-sensitive recording materials for the recording process, leuco coloring-type heat-sensitive recording materials providing excellent color density and coloring speed are mainly used.
Also, as an other process, there is known a process of heating a heat-sensitive recording material having a layer composed of a diazo compound, a coupling component, and an alkali generating agent or a coloring aid in order to conduct recording, and thereafter irradiating the recording material with light to decompose the unreacted diazo compound and stop the coloring, as disclosed, for example, in Japanese Patent Application (OPI) Nos. 123086/82, 125092/82 (corresponding to U.S. Pat. No. 4,411,979), etc. (the term "OPI" as used herein refers to a "published unexamined Japanese patent application").
On the other hand, Japanese Patent Application (OPI) No. 190886/84 (corresponding to U.S. patent application Ser. No. 600,267 filed Apr. 13, 1984) discloses a heat-sensitive recording material having an improved storability (shelf stability) using a microcapsule.
When the recording material is heated, the coloring component contained in the microcapsules permeates through the capsule wall to the outside thereof, or the other coloring component existing outside of the microcapsules permeates through the capsule wall into the capsule, thereby causing coloring in each case.
In accordance with a microscopic investigation, etc., it has been found that the coloring reaction in fact mainly occurs in the microcapsules. Accordingly, the reaction components before and after typewriting or writing are separated by the capsule wall, whereby the resistance and stability greater than those of the known heat-sensitive recording materials having a protective layer provided thereon.
However, since the microcapsules have an inherent tendency to be collapsed by pressing, it sometimes happens that the microcapsules are collapsed by unexpected pressing or during processing or handling of the recording material, or during heat recording using the recording material, to cause undesirable coloring.